Rotary cylinder locks which are well known comprise spring-loaded two-piece tumbler pins disposed in bores running radially to the cylinder core and cylinder housing. These pins are positioned by a flat key to permit free movement of the cylinder core, the key being introduced into the key channel of the cylinder core to position the correct alignment of the tumbler pin rows by means of recesses in the pile surfaces thereof. Different locking possibilities are achieved in locks of this type having a given diameter of the cylinder core and the same cross section of the key channel, by the fact that the recesses in the lateral faces of the keys have differing depths and the inner pins of the two-piece tumbler pins are designed with different lengths.
Another increase in the locking possibilities can be achieved by designing the distance between the several tumbler pins at different lengths. Furthermore, the axial distance of the first tumbler pin from the key stop at the face of the inner cylinder can also be changed. It is further known from Swiss Pat. No. 432,279 to increase the number of locking possibilities by changing the radial distance of the key channel from the surface of the cylinder core.
Nevertheless, the number of possible locking differences according to the methods mentioned and so far known is often unsatisfactory in the case of locking systems for large buildings, such as factories, hotels or banks, where all or a majority of the locks are operated by master keys and where specific groups of locks and/or single locks are operated by auxiliary or single keys differing from each other and from the master key. In such locking systems it is often necessary to omit tumbler pins from certain locks, i.e. to equip only a part of the existing bores with tumbler pins. This, however, results in a lessening of the security value of a lock.